The Community Youth Development Study: A Test of Communities That Care Abstract This five-year competing renewal will assess the long-term effects of the Communities That Care (CTC) prevention system. The CTC system is a strategy for mobilizing communities to use prevention science to plan and implement strategic community prevention services. Non-experimental evaluations of CTC suggest that it can assist communities to develop more effective prevention service systems and reduce adolescent health and behavior problems (Arthur et al., 2003;Feinberg et al., 2005;Harachi et al., 1996;Jensen et al., 1997). The current study is the first randomized controlled trial of CTC's efficacy. The CTC system is being implemented with fidelity in the intervention communities of the current study. The study is currently showing early effects on risk exposure and the initiation of delinquent behavior after three years of CTC implementation. The proposed renewal will assess the effects of CTC on key aspects of community prevention service systems and on adolescent drug use, delinquency, violence and risky sexual behaviors nine years after its initiation and four years after study-provided resources supporting CTC end. The Community Youth Development Study is an experimental test of the Communities That Care (CTC) prevention planning system. It is designed to find out if communities that use the CTC system can improve the public health by reducing rates of adolescent drug use, delinquency, violence, and risky sexual behavior when compared to communities that do not use this approach.